1. An awful meal.
2. A food that literally tastes fecal.
3. A complex dish made with painstaking care but has catastrophically disappointing flavor.
4. Absolutely not a delicacy

The term is used so as not to offend the cook. Politesociety tells us that it is rude to be brutally honest when asked how enjoyable a particular meal was. Polite society also tells us it is rude to correct someone's mispronounciation of a word. So, while you said "defecacy," he or she will think you meant "delicacy" but will be too polite to correct you. You can be honest say the meal tasted like a shit but the cook will believe you loved it. Everybody wins.

Q: "...So, did you like the chocolate-marshmallow & cheese meatloaf I made special just for you?"